Telegraphic transmission apparatus



H. E. BRAIN TELEGRAPHIC TRANSMISSION APPARATUS Aug. 14, 1945.

Filed Sept. 11, 1942 5 Sheets-Sheet 2 Ijzuelvizoz' J5EE, Bra/aw jy 4 wmmu rm m Filed Sept. 11, 1942 5 Sheets-Sheet 3 haelii or Eire/4:10

ug. 14, 1945- H. E. BRAIN 2,382,127

TELEGRAPHIC TRANSMISSION APPARATUS Filed Sept. 11, 1942 5 Sheets-Sheet 4 I222 11 can/Z02 Aug. 14, BRAlN TELEGRAPHIC TRANSMISSION APPARATUS Filed Sept. 11, 1942 5 Sheets-Sheet 5 Izwezo-ibr J1, Bra IJ-(z/ Patented Aug. 14, 1945 2,382,127 TELEGRAPHIC TRANSMISSION APPARATUS Harry Edgar Brain, London W. o. 1, England, assignor to The Automatic Telegraph and Radio Transceiver Company Limited, London, England Application September 11, 1942, Serial No. 457,989 In Great Britain December 30, 1941 2 Claims.

character or representation thereof and mounted to be movable independently of one another to bring about the actuation of generating contacts in a manner which corresponds to the particular code character selected for signalling.

The invention also consists in apparatus according to the preceding paragraph wherein the said members are axially disposed upon a common axis and the code character representations are provided upon arcuate arms at the outer ends of radial arms pivotal about said axis, the arouate arms being arranged in axial alignment and forming in effect segments of a cylinder, the axis of which is the axis referred to.

The invention also consists in apparatus according to the preceding paragraph wherein the said members are actuated from a disc mounted for oscillation and operatively associated with contacts which serve to cause power means to be brought into operation to control the return movement of said members.

The invention also consists in apparatus according to the preceding paragraph wherein the said members are actuated from the disc through the medium of a rod arranged to extend transversely across the member and pivotally mounted for movement about the axis of rotation of the disc.

The invention also consists in telegraphic transmission apparatus having the further features hereinafter described or indicated.

In the accompanying drawings:

Figure 1 is a side elevational view, somewhat diagrammatic, of a transmitter in accordance with the invention and showing the cam disc in its normal at rest position.

Figure 2 is a similar view to Figurel but showing the cam disc moved into the operative position during the generation of a code character. Figures 3, 4 and 5 are side elevational views, generally of a diagrammatic character, and illustrating in its several operative positions, the

mechanism employed in accordance with the invention to bring about automatically and by a definite time delay first the cessation of the paper I feed and then the shutting down of the motor,

Figure 3 showing the parts in the normal inoperative position of the mechanism in which the motoris stationary and the telegraphic instrument idle, Figur 4 showing the position of the parts during the generation of a code character and Figure Ershowing the position of the parts when after a certain time has elapsed since the transmission of a code character the rotary cam member is about to occupy a position in which the electrical contacts controlling the operation of the paper feed mechanism will automatically be broken, so that the feeding of the tape ceases, and

Figure 6 is an end view of the mechanism as seen in Figures 3 to 5 and shown connected with the shaft driven by the electric motor by which the paper feed mechanism is driven and which carries the armature of the electro-magnet by which the oscillatory movement of the crank disc is effected.

In carrying the invention into effect in one convenient manner, a telegraphic impulse generator or code transmitter is provided comprising a suitable framework or casing I which may resemble that of a typewriter and has a keyboard 2 on which there are assembled a plurality of character keys 3 each connected to its own lever arm 3a which extends horizontally across the bottom of the casing to the opposite end thereof where the key levers are pivotally mounted, as indicated at 3b, so that upon a character key being depressed its particular lever will swing downwards about its pivot.

Provided also within the casing at one side thereof and above the key levers there is a disc 4 mounted for angular rotation or oscillation about an axis 5 perpendicular to the plane of 'movementof the key levers and forming a crank disc to which there are connected, at circumferentially spaced points, as indicated at 6 and I, one end of two rods 6a, la, the opposite end of which rod la is connected to a second disc 8 mounted directly above the crank disc 4, while the opposite end of the other rod 6a, which extends horizontally from the first disc towards the front of the casing, is supported upon a plate 9 which extends transversely across the casing so as to depend from a horizontal pivot 9a and be situated in front of the forward ends of the key levers. 1 u

of the apparatus.

Mounted upon the casing there are two laterally spaced sets of contacts indicated generally at l and II and constituted by contact strips l2 grouped at their upper ends upon insulated blocks l2a, in the manner of a pile-up, so that the contact strips depend from their supporting blocks and have their free ends disposed adjacent to the sides of the crank disc 4.

The sets of contacts In, H are disposed on opposite sides of the crank disc. The set of contacts H) which is disposed on the side of the crank disc 4 remote from the keyboard is composed of two pairs of laterally adjacent strips l3, l4, of which one pair l3 serves, at the appropriate moment, to complete the electrical circuit to the aforesaid electro-magnet 8a and may be known as the segment-clutch contacts, while the other pair of contact strips 14 serves to connect the generator to the transmission line and is known as the line contact. The actual contacts, of course, are situated at the free ends of the strips and are indicated at Ha, Ha, 45a and Ilia.

The set of contacts H which is disposed on the side of the crank disc nearest thekeyboard is composed of three laterally adjacent strips IS, the centre one of which is always in contact with either one or the other of the outer strips so that in eflect this assembly or contact strips is in the form of a simple change-over switch. This set of contacts also includes a laterally adjacent pair of contact strips I6 which constitute the "line start contacts of the apparatus.

Associated with each set of contacts there is a pin l1, l8 arranged in engagement with the periphery of the cam disc for operation in the manner to be described later.

The generating contacts l9 are provided upon an insulated block 20 situated above a plurality of axially aligned arms 2| which are made to form electric conductors and are connected in the electrical circuit of the apparatus and which arms extend upwardly from the outer ends of a series of levers Ila, rigid with the arms, and the number of which corresponds with the number of key levers so that there is one such arm to each key lever and connected to the latter by a. link 2 lb. Each said arm 2| is of arcuate shape and has one or more elevations Me on its outer edge corresponding to the elements or a particular code character so that each arcuate arm is representative of one code character.

The arcuate edges of the said arms 2| are struck from a common centre which corresponds to the axis 2 Id about which the levers 2la which carry the arms pivot, so that the arcuate arms may be regarded as segments of a cylinder the axis of which is the pivotal axis Zld of the radial lever arms which carry them. This axis, as shown, is situated below and horizontally spaced forwardly from the axis of rotation or the crank disc 4, and mounted so as to partake of the angular movements of the crank disc there is a shorter lever 22, or which there is a counterpart at the oppoiste side of the casing, so that the two such levers 22 may carry between them at their outer and free ends a rod 22a which extends transversely across and in contact with the top edges of all the longer levers Zia which carry the arcuate arms. Each of the latter is formed with a tongue 2le projecting forwardly from its inner edge so as to form at the Junction of the arm with its lever a fork 2|} which lies electromagnet 8a included in the electrical circuit opposite the rod 22a and the purpose of which will be described later.

Referring again to the crank disc 4, the latter is provided around its periphery with a shallow 5 radial recess lBa with which the outer end of the pin l8 associated with the transmit-receive switch and the "line start contacts normally engages (that is when no character key is depressed) to cause the transmit-receive switch to be on the receive side and the line start contacts to be open. Diametrically opposite this recess, or substantially so, the crank disc is provided in its periphery with another radial recess Ha in which the pin ll associated with the set of contacts on this side of the disc normally engages so as to lie in the path of the upper and inclined end edge Nb of an arcuate lip Ilc projecting from the outer face of the disc at right angles to the plane thereof and the lower end edge 11d of which lip is also inclined in the same direction as its upper end edge and terminates at another radial recess lie in the peri hcry of the disc on this side thereof.

It should be stated here that the pin l'l associated with the pile-up which includes the line contact is carried at the outer end of an arm llf projecting forwardly from the foremost contact strip I4 so that the pin normally extends into the upper radial recess Ila on this side of the crank disc so as to lie in the way of the top edge Nb of the arcuate lip Ho and as this edge llb is inclined upwardly from the outer side surface to the inner side surface of the lip it follows that upon the crank disc 4 being moved upwards on this side the pin I! will, during such upward movement, move outwards along the top inclined edge of the lip until it eventually comes up against the outer side surface of the lip and in this condition the segmentclutch and the line contacts will be held closed and their contact strips will be tensioned. During the continued upward movement of this side of the crank disc 4, the peripheral recess He at the lower end of the lip l'lc is brought opposite the pin ll. At this moment the pin IT will spring inwards into this recess to lie in the path of and beneath the bottom end edge lld of the lip and due to the inclination of this edge, on the return angular movement of this side of the disc 4 and which now takes place, the pin is cammed inwardly through the recess towards the centre of the crank disc and engages the inner concave surface of the arcuate lip. In doing so the contacts of this pile-up which, due to the releasing of the pressure on the contact strips, will have been opened when the pin l1 leaves the outside edge of the arcuate lip He and enters the recess He will be pulled further apart and will remain open until at the termination of the return movement of the crank disc, the recess Ila at the top of the lip He is brought opposite the pin I! when the contacts will again be permitted to close and their contact strips restored to their normal positions in which the pin I! again lies in the path of the top inclined end edge ill) of the arcuate lip, ready for the next oscillation of the crank disc.

In the operation of the apparatus therefore, 0 upon a character key 3 being depressed, the lever 3a connected thereto will be moved downwards about its pivot 3b at the rear end of the casing and at the same time the particular arcuate arm 2| associated with this lever will be raised and in so doing the rod 22a on the short levers 22 referred to will be raised and eventually, during the upward movement of this arm, this rod, which of'course leaves the tops of the other arcuate arms corresponding to the other code characters, enters into engagement with the fork 21 of the raised arcuate arm. Due to the raising of the short levers 22 the crank disc 4 will be rotated clockwise and in doing so the pin I! associated with the pile-up which includes the "line contact Ma will enter into engagement with the outer side surface of the arcuate lip We on the crank disc 4 in the manner above described so that the two contacts I3a and Ma of this pile-up will be held firmly closed. Simultaneously with such firm closing movement of these contacts 13a, I411 the pin IS on the opposite side of the crank disc will be pushed out of its recess l8a to cause the transmit-receive switch 15a to be changed over to the transmit position and the line start contact 16a to be closed. When during the operation of'the crank disc 4 clockwise the recess He at the bottom end of the lip H is brought opposite the pin I! on this side of the disc and which pin is now in engagement with the outer side surface of the lip, the pin will spring into the path of the lip. This position corresponds to the fully depressed position of the character key, in which the electro-magnet 8a will have been energised by the previous closing of the segment-clutch contact l3a, so that immediately the key is released by the operator the arcuate arm 2|, together with the transverse rod, now engaged in its fork, are moved positively downwards by the consequential rotation of the crank disc in an anti-clockwise direction so that the pin I1 is forced into the recess at the lower end of the lip and contacts with the inner surface of the lip during the continued rotation of the crank disc anti-clockwise. Immediately the pin IT is moved inwards in the recess He the contacts |3a and Ma will be opened and will be maintained opened in a positive manner by the engagement of the pin I! with the inner surface of the rib. The contacts Ma of the pile-up are, as stated, the line contacts of the transmission circuit while the other contacts I30. serve to control the energisation of the electro-magnet 8a which, when energised, causes the disc 8 which is mounted above the crank disc 4 and is connected thereto by the said crank rod 1a to be rotated anti-clockwise. When the electro-magnet But is energised therefore, the rotation of the crank disc 4 in the return direction, in which the arcuate arm 2| is lowered, will take place under the control of the'upper disc 8 and as the latter is arranged to be driven in synchronisation with the movement of a recording gear (indicated generally at 23 in Figure 6) by which a record of the signalled characters is taken, it follows that the movement of the arcuate arms 2| in the actual generation of the code characters, which takes place during the upward movement of the arms 2|, will be synchronised with that of the recording gear. As the lever Zla carrying the arcuate arm is restored to its low ered position the transverse rod 22a which moves therewith will move out of the fork 2h at the junction of the arm with its lever and will be brought to rest when lying across the tops of the rear end of all the character key levers 3.

At the commencement of the oscillating movement of the crank disc 4 the other rod 6a connected therewith and having the stops 6b, 6c thereon on opposite sides of the plate 9 and which rod extends to the front end of the character key levers moves rearwards and as it does so the plate 9 mounted in front of the key levers swings rearwards about its pivot 9a (due to thee engagement of the stop 61) with the plate) so that a flange 9b projecting rearwards from its lower and free end lies beneath the forward ends 30 (Figure 2) of all the character key levers which have not been depressed. Consequently these levers are locked against actuation while a character key is depressed and are not freed foractuation until on the return of the depressed character key lever to its normally raised position the plate 9 is rocked forwards about its pivot (by the engagement of the stop with the plate) and the flange 9b thereon is withdrawn from beneath the front ends 30 of the character key levers.

The invention also extends to the provision of an automatic mechanical switch mechanism, as illustrated in Figures 3 to 6, adapted automatically after a definite time interval to stop the feeding of the paper or tape in a recording mechanism (which may be the recording mechanism embodied in the telegraphic transmitting instrument above described for making an ink record on the paper or tape of the transmitted matter, or which may be incorporated in another form of transmitter employing an electric motor controlling the mechanical functions involved) and after a definite longer time interval to s-h'ut-down an electric motor controlling the mechanical functions involved in the instrument, whereby the instrument is rendered completely inoperative or dead. For this latter purpose the mechanism in question includes a pair of contacts 24 which are so connected in the circuit of the transmitting instrument that upon the initiation, or at the commencement of transmission these contacts are closed and are maintained closed until a definite time interval has elapsed since a character was transmitted. In other words, once transmission has commenced these contacts 24 (which if opened or broken shut-down the electric motor) are held locked in the closed position until the definite time interval referred to has elapsed when the contacts will be automatically and mechanically broken in the manner and by the means to be described. For the purpose of stopping the paper or tape feed the switch mechanism incorporates another pair of contacts 25 connected in the electrical circuit of the instrument such that they influence the operation of the recording mechanism (the paper or tape feed mechanism 23) so that if the contacts 25 are broken, the recording mechanism ceases to function, and an electromagnet 26 which is connected in the electrical circuit of the instrument so as to be energised whenever one of the elevations 210 on the arcuate oscillatory lever arms 2| moves across its generating contacts IS in the generation of a code character.

The armature 26a of the electro-magnet 26 is linked to the arm 21a of a double-arm lever 21 by the link 26b, which lever is pivotally mounted at 21b and has a tension spring 210 connected to the end of its other arm 21d which spring tends to maintain the lever arm 21a in a raised position in which the periphery of a cam disc 28 is maintained in contact with the periphery of a friction disc 29 fast upon a sh'aft 30 which constitutes the driving member of the automatic mechanical switch mechanism and is driven from the electric motor (not shown).

The cam disc 28 has two similar part cylindrical peripheral surfaces 28a separated by diametrically opposite recesses hand rigid with the disc there is a diametral block 280 providing, on its opposite faces, flats 23d with which the flat free end portion No of a strong leaf spring 3| tends to engage to maintain the leading portion of either one or the other of the part cylindrical cam disc portions 28a immediately opposite the periphery of the friction disc 29, the leaf spring being anchored to the base of the lever along its opposite end portion 31b. The cam disc is rigid with a central axle pin 23e by which the cam disc and block 260 are pivotally mounted in the side walls 210 of the lever and at its outer end the lever am 213. carries a pin 32 which, when this lever arm is in the extreme lowered position in consequence of the armature 26a being attracted on account of the coil of the electro-magnet 26 being energised, is arranged to press against the upper contact strip of th'epair of contacts and close these contacts. The periphery of the friction disc 29 is intended to have frictional driving engagement with the cam disc 28 when one or the other of the part cylindrical surfaces 28a of the cam disc is in contact with the friction disc 29 and in order to afford increased frictional engagement between these parts theisame may be formed with interengaging bevelled surfaces 33. When, however, during the operation of the mechanism and rotation of the cam disc 28 one or the other of the recessed p rtions 28b of the disc is brought to lie immediately next to the friction disc 29, the frictime! driving connection between the two discs will be discontinued and the arm 21a of the lever 21' will move into its extreme upper position in which the pin 32 leaves the contact strips of the contacts 25 and the latter are opened and, accordingly, the recording mechanism stops.

The friction disc 29 is, as stated, fast upon the main driving shaft and this shaft also carries fast thereon one of the gear wheels 34 of a hypoid gear, the other gear wheel 34a of which is driven by the gear wheel 34 and provided upon the driven shaft 23a of the recording mechanism. The main driving shaft 30 also carries the electro-magnet 3a referred to above and provided to drive the crank rod 1a to produce the return movement of the segment arms 2| in an anti-clockwise direction and the shaft also carries, but loose thereon, a ratchet wheel 35 with the teeth 35a of which a pair of pawls 36, 36a are adapted to engage to produce at the required moments a stepwise rotation of the ratchet wheel in a direction (clockwise) opposite to that in which the ratchet wheel is rotated by the shaft 32 when, in the energised condition of the electro-magnet 26, the pawls 36 and 36a are withdrawn from engagement with the teeth of the ratchet wheel due to their being engaged at this time by an overhead arm 31 on a rod 31a upstanding from the arm 21a of the lever 21 and secured thereto. In this condition, therefore, the ratchet wheel is free to rotate anti-clockwise with the shaft. Thepawl 36 is pivotally mounted at the free end of a lever arm 38 pivotally mounted upon one side of the main driving shaft 30 about an overhead pivot axis 33a and restrained by a tension spring 331) normally to approach the ratchet wheel so that this pawl will engage with one of the teeth thereof, the pawl 36 being in turn normally constrained to engage the teeth of the ratchet wheel by the action of a spring 36c. A fixed stop pin 39 serves to locate the lever arm 38 in its normal forward position with respect to the ratchet wheel. Thenother pawl 36a is pivoted upon a fixed part of the mechanism and, as already indicated, the overhead arm 31 of the upstanding rod 31a is arranged to lie in the path of the free ends of the two pawls so that both are depressed and moved out of engagement with the teeth of the ratchet wheel when, as a consequence of the electro-magnet 28 being energised, the arm 21a of the lever 21 is moved to a lowered position against the action of its restraining spring 210.

The ratchet wheel is provided with a pin 43 situated near the periphery of the ratchet wheel to lie in the way of an insulated block 4| provided at the upper free end of a spring strip 41a secured upon a fixed insulated block 42 to which the spring contact strips 24a carrying the contacts above referred to are secured, the contact strip 24a nearest the spring strip 4la being provided with an enlarged opening 24b through which a pin 24c fast on the spring strip Ha passes freely so that its free outer end lies against the outermost contact strip 24a. The spring strip 4la is biassed to assume normally a position away from the contact strips 24a such that the contacts 24 will be closed, but it will be seen that upon the pin 40 on the ratchet wheel arriving against the insulated stop 4| and exerting pressure thereon the spring strip 4la Will be moved towards the contact strips 24a and as a consequence the pin 240 will exert pressure on the outside contact strip 24a and open or break the contacts 24, thereby releasing the lock in the motor circuit involved thereby. This, however, will only occur when, during a period when the instrument is idle, the ratchet wheel is advanced tooth by tooth clockwise by a pin 29a, extending from the friction disc 29, contacting the lower free end of the lever arm 38 to knock it aside momentarily (to the right as seen in Figures 3 to 5) thereby freeing the pawl 36 so that it may, on the return of the lever arm, engage the ratchet wheel and advance it one tooth, when the ratchet wheel is held stationary by the engagement of the retaining pawl 36a until the lever arm is again knocked aside by the pin 29a after the completion of another revolution of the friction disc counter-clockwise.

Figure 3 illustrates the automatic switch mechanism in the position of the parts corresponding to the shut-down or completely idle condition in which the lock 24 on the electric motor circuit is broken and the contacts 25 are open so that the electric motor and the recording mechanism are stationary. In this position the lever 21 is in the position, maintained by its restraining spring 210, in which one of the depressions 28b on the cam disc is against the friction disc 29, but it will be noticed that the flat part 3la of the leaf spring 3| has been deflected to the position in which it presses firmly against the nearest corner of the diametral block 28 so that immediately the lever arm 21 is lowered, in consequence of the electro-magnet 26 being energised and the armature 26a, thereof attracted, the cam disc will at once be snapped over by the spring 3| to the position in which the uppermost part cylindrical surface 28a lies opposite the friction disc 29. The lever arm 38, in this condition of the parts, is in its normal forward position against the stop pin 39, in which the pawls 36, 36a are engaged with the teeth 35a of the ratchet wheel 35, and the pin 40 on the latter is in the position in which it engages the insulated block 4| to cause the contacts 24 to be broken and held thus. It will be realised, having regard to Figure 3, that as the pawl 36 on the lever 38 and also the pawl 36a are now in engagement with the ratchet wheel (since the electro-magnet 26 is now deenergised and the lever 21 is in its uppermost position) the latter is prevented from turning anti-clockwise about the shaft 30 by the action of the now compressed spring Ma but will be freed so as to turn immediately the electro-magnet 26 is again energised and the pawls, accordingly, moved out of engagement with the ratchet teeth.

Figure 4 illustrates the position of the parts when during the transmission of a code character the electro-magnet 26 is energised, the armature 26a is attracted and the arm 21a of the lever 21 is as a result moved to its extreme lowered position against the action of its spring 210. In this position the contacts are closed, the cam disc 28 is maintained out of contact with the friction disc 29, the overhead arm 31 functions to hold the pawls 35, 36a out of engagement with the teeth of the ratchet wheel and the contacts 24 are closed so that the motor circuit is now locked in the condition in which the motor operates continuously until the lock is broken. In this position therefore, the ratchet wheel will be free to turn anti-clockwise with the shaft until the pin 49 reaches the position shown against the insulated block 4| when the pin is prevented from further anti-clockwise rotation and is in its zero position.

Figure 5 shows the position of the parts when current has ceased to flow through the electromagnetZt so that the lever arm 21a is in the raised position in which the ratchet wheel is again held against rotation anti-clockwise with the main driving shaft 30 and the contacts 25 are still closed since although current has ceased to flow in the electro-magnet 26 one of the part cylindrical surfaces 28a is in contact with the friction disc 33 and as the motor is still running the cam disc 28 will be rotated until such time as one of the depressions 28b has been brought opposite the periphery of the friction disc. When this occurs the lever arm 21a will move to its extreme upper position, as seen in Figure 3, in which no further rotation of the cam disc can take place and the contacts 25 are broken, This, however, will only occur after the elapse of a definite time interval since a code character was generated and this time interval is equivalent to the time it takes for the cam disc to make an angular movement equal to the extent of one of the part cylindrical surfaces 28a. It may be pointed out here that during th transmission of characters the armature 26a will be continuously oscillated, depending upon the number and nature of the projections Zlc on the various segment arms 2!, and the electro-magnet 26 energised and de-energised on account thereof, but in no instance, during generation of a code character will the extent of angular movement of the cam disc equal the extent of one of the surfaces 28a. In other words, the dash elements of Morse code, as represented by the projections 210 on the segment arms is much shorter in length than the length of one of these surfaces 28a. The dot element, also represented by a projection 2|c is, of course, shorter in length than those projections which are representative of a dash element of the code. Although the contacts 25 will now have been broken and the paper feed ceased the electric motor will still be running and the shaft so, as a consequence continues to rotate anticlockwise. For each complete revolution of the friction disc 33 the lever arm 38 will be knocked aside (to the right as seen in Figures 3 to 5) by being engaged by the pin 29a and by its pawl 36 advance the ratchet wheel one tooth in a clockwise direction until after the elapse of a certain time interval, equivalent to the number of teeth there are in the ratchet wheel, the pin 29a will be brought up against the underneath side of the insulated block 4| and when moved past the same, due to the ratchet wheel being advanced another tooth, will push the block aside to compress the spring arm Ma and break the lock on the motor circuit by opening the contacts 24.

I claim:

1. An electro-mechanical switch comprising circuit controlling contacts movable into closed position, a motor driven friction disc, a cam having a cylindrical portion for frictional driving engagement with said friction disc and a recess therein, a lever movable to a position to close said contacts and rotatably supporting said cam, means to operate said lever in one direction to close said contacts, the cylindrical portion of said cam being positioned to operatively engage the friction disc upon movement of said lever and acting to hold said lever in contact closing position throughout the period of rotation of said cam by frictional engagement with said disc, and means operative, when said cam is rotated through an angle suiiicient to present said recess to said friction disc, to operate the lever in the opposite direction whereby the contacts may open.

2. An electro-mechanical switch comprising circuit controlling contacts movable into closed position, a motor driven friction disc, a cam having a cylindrical portion for frictional driving engagement with said friction disc and a recess therein, a lever movable to a position to close said contacts and rotatably supporting said cam, means to operate said lever in one direction to close said contacts, means operative upon movement of said lever to contact closing position to rock the cylindrical portion of said cam into operative engagement with the friction disc, said lever being held in contact closing position by said cam throughout the period of rotation of said cam by frictional engagement of the cylindrical portion with said disc, and means operative, when said cam is rotated through an angle sufficient to present said recess to said friction disc, to operate the lever in the opposite direction whereby the contacts may open.

HARRY EDGAR BRAIN. 

